1. Technical Field of the Invention
The present invention generally relates to power management sections comprising methods of monitoring and switching between external and internal power sources in a system, and means of facilitating the recharge of rechargeable internal power sources such as battery packs. These power management sections are adapted to sense when a source has been coupled to an input terminal and also to recharge, when appropriate, said internal power sources. Such power management systems are typically used in electronic devices, such as notebook computers.
2. Description of Related Art
Power management sections facilitate the powering of systems and devices that require a stable output voltage from one of a plurality of power sources. Many electronic device applications require these power management sections as they are adapted to receive power, for example, from an AC wall source or an external or internal DC source. Power management sections have been developed to control and regulate power to a system from several sources. Often, these systems can be powered from one of several sources, including an AC source, an internal DC source, such as a battery, or an external DC power source such as a car or airline adapter. The battery packs used in these systems are usually rechargeable types, such as NiCd, NiMH, Li-Ion, and Li-Pol battery packs. In addition to powering the system, AC or wall sources or external DC sources also are used to recharge these battery packs.
In notebook computer systems, the primary function of the power management section is to charge the battery pack and guarantee power continuity to the system. These functions are often implemented with the use of dedicated integrated logic circuits (“ICs”) or a combination of micro-controller and discrete analog and digital components such as oscillators, comparators and logic gates. In order to perform the power switch and battery pack recharging functions, conventional circuit topologies use a set of power switches (usually MOS transistors) and discrete diodes. Typically a power diode is required to isolate the adapter from internal nodes, and the MOS transistors are controlled to isolate the AC adapter from the battery or load. A buck converter uses the adapter power to recharge the battery.
Usually the input power is switched to the system when the AC adapter voltage is above the target charge voltage. There are some instances, however, when the AC adapter voltage must be switched to the system even if it is lower than the battery voltage. This condition is normally referred to as “airline” mode operation and is required when the end equipment must be powered from an external supply which voltage is lower than the pack voltage. Disadvantageously, conventional topologies are unable to implement airline mode. In such cases, the system continues to run off the higher voltage battery pack even with the external DC source or AC adapter wall source connected to the device, thus discharging the battery pack until the pack voltage matches the external supply voltage. To implement airline mode using conventional topologies at least 2 additional switches and external control logic must be added to block the conduction path from battery to system. This increases the system cost and decreases overall system efficiency, as the series resistance from the battery pack to the system is increased.